The present invention relates to a method of driving a thermal head used for thermal recording.
In a thermal recording apparatus, for example, a thermal head in selectively driven to cause a portion of a sheet of thermosensitive paper placed in contact with the thermal head to generate color to record information thereon. Ordinarily, a number of heating elements are aligned in the thermal head. It is not efficient to separately drive these heating elements at different timing, in view of recording speed requirements. Accordingly, in ordinary recording apparatus, a plurality of heating elements are simultaneously driven. To this end in such an apparatus, a serial picture data is inputted to a shift register and then converted therein into parallel picture data in response to which the heating elements are driven. In the case where the heating elements are grouped and to be driven group after group a number times per one line in such an apparatus, however, it is necessary to replace old picture data set in the shift register by new data a corresponding number times for one line.
To this end, a counter has been provided in the conventional apparatus to count every time pieces of picture data corresponding to the number of the heating elements to be driven simultaneously have been inputted to the shift register and produce a signal indicating the completion of setting of data. In response to the set completion indication signal, the transfer of the picture data to the shift register is stopped and then restarted after the driving of the concerned heating elements has been attained. The replacement of picture data in the shift register has been achieved in this manner.
In such a conventional thermal head driving method, however, there is a drawback that as the number of the heating elements to be simultaneously driven increases according to demands for high speed recording, this increases the counter size and accordingly increases the cost of the entire apparatus.